This invention generally relates to the field of disk drives, and more particularly to forming optimal structures for bonding in a head gimbal assembly using anisotropic conductive adhesive.
With the rapid progress of miniaturizing and thinning technology for electronic devices, high-density inner wiring systems including flex-print circuit (FPC) have become essential. At the same time, micro-connecting technology for the connection of FPC with other electronic parts, such as the traces on a magnetic head suspension assembly, is indispensable.
Traditionally the FPC is capable of adopting ultrasonic bonding. The connecting terminals of the FPC are plated with gold; the flying leads of the FPC are aligned with and pressed to the bonding pad on the suspension with sufficient force to keep the alignment and atomic interdiffusion of the flying leads and the underlying metallization, which process ensures the intimate contact between the two metal surfaces. However, the pressing of the flying leads of the FPC entails complex processing, and ultrasonic bonding to different bonding pads is very difficult to contact. Moreover, bonded parts cannot be separated in the future to be reworked without damaging the FPC or the suspension.
Alternatively, FPC can be solder-bound using solder bumps produced by, for example, plating processes, for interconnections. However, this process requires forming metal cores and solder bumps for soldering. The metal cores incur extra expenses, and soldering has to be performed at high temperatures typically over 180 degrees Celsius.
Furthermore, both ultrasonic bonding and soldering are becoming increasingly expensive because of high cost of labor and parts of the FPC. There is therefore a need for a bonding method which achieves a stable, reworkable connection without complicated processing.
The present invention features a novel structure and method for using anisotropic conductive adhesive to bond parts in a head gimbal assembly (HGA) comprising the slider and the FPC.
It is an object of the present invention to overcome the complexities of prior art approaches of ultrasonic bonding and soldering. This invention will alleviate the difficulty of one-time bonding in the case of ultrasonic bonding, and avoid high-temperature bonding required in soldering.
It is another objective of the present invention to reduce the bonding pad size and floating capacity.
Yet another objective of the present invention is to reduce the space between bonding pads to accommodate the trend toward miniaturization of the disk drives and the head assemblies.
A further related objective of the invention is to improve capacity in the bonding process. Reduced sizes of the bonding pads, reduced spacing between the bonding pads, and elimination of additional interconnecting components will contribute to reduce parasitic capacitance. Reduced capacitance will improve the rise and fall time of the electronic signals, thus increase the data rate of the hard disk drive.
In one aspect, the invention relates to adding a conducting structure lodged between the two sections of an overcoat layer of a FPC to enable bonding between the FPC and a contact pad in a HGA using anisotropic conductive adhesive, such as anisotropic conductive film (ACF). The conductive structure can be shaped as a ball and plated with gold, or it can of other types of conductive materials. The overcoat layer may overlap a portion of the top surface of the conductive pad, or the overcoat layer may not touch the conductive pad at all. Alternatively, the conductive structure may be a filler comprising an electrically conductive material completely filling the space between the two sections of the overcoat layer and above the conductive pad. In one implementation, the overcoat layer may comprise one section, or it may be of ultra thinness of less than 10 xcexcm.
In another aspect of the invention, a conductive layer of the FPC may be bound to the contact pad directly by anisotropic conductive adhesive material without an overcoat layer in between.